1. Assume two types of PCa exponential growth rates, a fast and a slow. The growth rates are 0.30 and 0.15 cells per month and the horizontal axis is months.
2. Also assume that at 1 million cells we can just start to detect a malignancy, say PSA rise and at 1 billion cells our poor guy is dead. These are used by Weinberg so they are reasonable.
3. We show the cell numbers and the two levels.
4, In about five years our aggressive type kills the patient. The slower type takes almost 12 years. In reality there may be multiple types which never kill a patient. But this is just an example.
5. Now assume we do PSA tests every 2 years, even more frequent than some of the "gold" standard studies, but worth a look.
6. From our model we may just detect a PSA change in the aggressive type at year 4 and we say don't worry, come back in 2 years. He never gets to come back, he is dead two months before his next test!
7. The slower growth may afford time under this protocol.
8. If we had tests every six months for this patient we most likely could have saved him.
This is the point I have been making. Namely in order to really do this study properly you need to separate types of PCa into pools and then do the analysis. To separate you must do much more frequent testing otherwise the poor fellow with the aggressive type will die and you will just consider the use of a PSA test as futile. The true answer is your testing methodology is futile.
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